The present invention relates to a security marker, and to an item incorporating a security marker. The invention also relates to a system for detecting a security marker.
Security markers are provided to enable an item to be validated. The need for security markers for valuable items, such as documents, is well known. Banknotes typically include advanced security features, such as watermarks, fluorescent inks, security threads, holograms, kinegrams, and such like. However, with advances in copying technology, it is becoming more difficult to provide security features, which are difficult to counterfeit, easy to detect, quick to detect in situ, and not too expensive to incorporate in an item.
Chemical and biochemical taggants (also known as labels, markers, or tags) are added to items as markers that can be detected to validate the items. However, to validate such taggants, the taggants typically have to be removed from the item and then analyzed. This is both time-consuming and expensive, which renders such taggants inappropriate for on-line, high speed examination.
Optical based techniques have been used for non-visual encoding of a range of products. One of the most widely employed optical labeling strategies uses fluorescent labels, for example labels printed using fluorescent ink or dye. Fluorescent materials emit light when excited by radiation of a particular wavelength. Information can be encoded by forming marks using fluorescent inks, which information can only be retrieved when the mark is illuminated with radiation of the appropriate wavelength. An example of a particular type of fluorescent ink is described in U.S. Pat. No. 5,256,193. JP 8208976; U.S. Pat. No. 4,736,425; U.S. Pat. No. 5,837,042; U.S. Pat. No. 3,473,027; U.S. Pat. No. 5,599,578; GB 2,258,659; U.S. Pat. No. 6,344,261; and U.S. Pat. No. 4,047,033 describe various security labeling and printing applications. However, known inks and dyes have the disadvantage that they have very broad spectra, which limits the number of inks and dyes that can be used in an item.